The Botany of Iceland - 01.12.1928, Side 68

392
JOHS. BOYE PETERSEN
proach f. producta with which they have this in coramon that part of
the median portion of the valve has parallel sides. V. Heurck Syn.
Pl. IV, flg. 1 b, on the other liand, bears no resemblance to the specimens
of f. ventricosa which I have seen. This form is evidently much less
common in Iceland than in Denmark. But few specimens were found
in the satnples mentioned.
Navicula mutica f. producta Grun. Cl. und Grun., Arct. Diat. p. 41.
Van Heurck Syn. Pl. X, fig. 20a.
Vestmannaeyjar L. 409.
The description in Arct. Diat. (1. c.) shows excellent agreement with
V. Heurck’s picture (1. c.) whereas Cleve’s description (Syn. I, p. 129)
»V. lanceolate, with broad truncate ends« seems to me to agree badly
with this form. I only found it in few specimens in the sample men-
tioned above.
— — f. minima Boye P. Boye Petersen 1915, p. 287, fig. 6.
E. Icel. L. 7, L. 40, L. 68, L. 77, L. 78, L. 92, L. 112, L. 114, L. 121
N. Icel. L. 135, L. 137, L. 179, L. 184, L.196, 217, L. 219, L. 243, 254 —
S. Icel. L. 381 — Vestmannaeyjar L. 400, L. 408, L. 409.
V. Heurck’s Types Nr. 113 mainly contains f. minima in a rather
pointed form. (A similar form often occurs in the Icelandic samples).
As a rule forma minima occurs in company with f. Cohnii with which
it is connected by forms showing a gradual transition. In a single sample,
however, I found f. minima alone (243).
It may perhaps be cjuestionable whether this form should be main-
tained as a separate forma, but, as mentioned, it may occur in the pure
form, without f. Cohnii being present, and in addition growths of f. Cohnii
are frequentlv found in which it will be useless to search for f. minima.
According to the data, its ecology would seem to be the same as that
of f. Cohnii.
— — f. quinquenodis (Grun.) N. nivalis Cl. Syn. I, p. 130; Boye Pe-
tersen 1915, p. 288.
E. Icel. 7 - N. Icel. 217.
I have only found this form in two localities in Iceland and very
few specimens of it. It is evidently much rarer in Iceland than in Den-
mark (Boye Petersen 1. c.). 0 strup (1918, p. 11) found it in 5 samples,
4 of which originated from hot springs. This would seem to indicate
that it is a southern form chiefly able to thrive in Iceland by the hot
springs. As a matter of fact one of the samples in which I found the
species was of a thermal nature (Nr. 217). However, this form is also
known from Greenland and Franz Josefs land, and not from hot springs.
-----f. rhomboidea Playfair. Playfair 1914, p. 112, Pl. IV, íig. 7.
Fig. nostr. 18.
E. Icel. 112 — N. Icel. 135, L. 184.